Tetrahedron Letters,Vo1.25,No.44,pp 5095-5098,1984 0040-4039/84 $3.00 + .Oo Printed in Great Britain 81984 Pergamon Press Ltd.

CATIONIC BENZOANNEL.9TION OF A(=TIVE METHYLENE

KETONES VIA OXOKETENDITHIO.ACETALS

Gurdeep Singh, Hiriyakkanavar Ila* and Hiriyakkanavar Junjappa*

Department of Chemistry, North-Eastern Hill University

Bijni Complex, Bhagyakul, Shillong 793003

Meghalaya, India

Summaryr o+Oxoketendithioacetals are shown to be useful intennediates for benzoannelation of <-methylene ketones by reactions with allylmagnesium bromide followed by cationic cyclizations of the resulting carbinolacetals.

Momatic annelation frznn aliphatic precursors constitutes an important

synthetic operation. Most commonly employed Robinson annelation' or modified

Diel's Alder react ion2 involve cyclocondensation of two fragments, one with

two and the other with fD,ur carbon atoms. Recently severa1 new approaches

involving the combination of bDth three carbon f ragments, one with two

1,3_electrophilic sites and the other with 1,3-dinucleophilic sites, have also

been reported. 3

The 1,3-electrophilíc fragments employed in these reactions

comprisep-dimethylaminoenones (la),

acetals (2),5a 3F

-silyloxyenones (lb)4'5b*5c and $-keto-

which can be easily prepared from active methylene ketones.

Cwdensation of la or Ib with 1,3-carbanionic species (or their synthetic -- equivalents) is reported ta give substituted benzene derivatives.

0 H

Y Kp’ X \ \ \__ _ R'

0 OEt

F + OEt \ \ ‘__/ R'

2 c X = -S-m-Bu

similarly, the nucleophilic additions of allyltrimethylsilyllithium5aor methyl-

allylmagnesium bromidesb on carbonyl carbon of 2 and Ib respectively followed -

by subsequent Lewis acid catalyzed cyclization also afford benzoannelated

products. Interestingly, the corresponding thiornethyleneketone (lc) did not -

give the expected benzoannelated product under identical reaction conditions. 5b

Our interest in6oxoketendithioacetals (3) as three carbon fragments

with well defined 1,3-electrophilic centres,for the synthesis of a wide variety

5095

5096

of heterocyclic compounds is well establishede6 They have also been shown to be

versatile intermediates for 1,3-carbonyl transposition in their reactions with

sodium borohydride' and organometallic compounds. 8 We were therefore prompted

to consider these intermediates as potential precursors for aromatic annelation

and our preliminary results on the conversion of 3 to 2 are reported in this

communication.

VJhen the allylmagnesium bromide was reacted with 2, the corresponding

carbinolacetal 5 was obtained in almost quantitative yield ( 7 95%); which

without further purification was cyclized in presente of borontrifluoride

etherate to give benzoannelated prcduct _ in 74% yield. The other benzoannela-

ted groducts and their yields are given in the table. when the allylmagnesium

bromide was similarly reacted with dithioacetals 31-1, th.e corresponding -- biphenyl derivatives Si-k and substituted toluene 51 were obtained in compara- -- - tively lower yields (39-45%).

Apparently the reaction proceads through intramolecular participation of

allylic double bsnd with the formation ,of carbonium ion intermediate 6 which

on loss of proton and methylmercaptan yields 2' Availability of active

methylene ketones with their wide structural diversity and their easy conver-

sion toa-oxoketen dithioacetals in one pot reaction, makes this method

attractive for the preparation of aromatic and bensoannelated products. It

is pertinent to note that earlier attempts for benzoannelation of cyclic

ketones via o-trialkylsilylmethyleneketones with either allylmagnesium chloride

or (allyltrimethylsilyl)lithium afforded low yields of benzoannelated products

along with other side p~oducts. 5b

-MgBr

;R , ether 1 \ \ -_c ‘3

4 -8

1 BF,.Et20/

C6Hô

- CH,SH

Sc heme

5097

Table

1 2

3 4 5

6 7 8

9 10 ll

12

s! 3!?

R R’ Prorluctb

S-b, n= 1 64

&H; n=l

l&H; -2 &OCH,; n-2

R”=H ti, R?H 45 R”=OCH, R”ZCI

Q, KOCH, 39 ti, Rh 40

ác n=l ; R’g H 54 Qi n=2; R%H 68 f& n=2; &OCH, 67

H3

-C,H, -CH, 40 a!

ayield of the pure fsolated poduct.

b Al1 the compounds were characterized by their spectral and analytical data.

5098

In a typical experiment, a solution of & (3.03g, 0.015 mol) in 20 ml o.?

dry ether was added ta a solution of allylmagnesium bromide (0.03 mol) in 50 ml

of ether at 0-5'C under nitrogen current. The reaction mixture, after further

stirring for 45 min, was decomposed by saturated ammonium chloride solution

(35 ml), extracted with ether, dried and evaporated to give crude carbinol 2

(3*6g, 95%) which was dissolved in dry benzene (50 ml) and BF3 etherate (2 ml),

and refluxed for 30 min. The reaction mixture after cooling was poured on

saturated NaHC03 solution, extracted with CHCl (2x100 ml), washed (H~O), Aried

and evaporated and the residue was passed through silicagel column (hexane as

eluent) to give _ (1.979, 74%) as viscous liquid (T.L.C. single spot); M+(mass)

m/zr (178): ior. (neat): 1580, 1440 cm"; 'H-n,m.r. (CCld) 5 1.80-2e25 (m, 4H);

2.32 (s, 3H, SCH3): 2.52-2.92 (m, 4H, CH2); 6,65-7.10 (m, 3H, aromatic).

Acknowledgement: G.S. thanks C.S.I.R.* New Delhi for a Senior Research

fellowship.

Referentes

1. D.L. Boger and M.D. Mullican, J. Org. Chem., 0, 5002 (1980) and referentes

therein.

2. (a) S. Danishefsky, C.-F. Yan, R.K. Singh, R.B. Gan-unill, P.M. McCurry, Jr.,

N. Fritsch and J. Clardy, J. Am. Chem. Soc., 101, 7001 (1979);

(b) S. Danishefsky, T. Harayama and R.K. Singh, J. Am. Chem. Soc., 101,

7008 (1979).

3. N. Takeuchi, K. Ochi, M. Murase and S. Tobinaga, J.C.S. Chem+ Comm., 593

(1980).

4. (a) T-H. chan and P. Brownbridge, J.C.S. Chem. Comm., 578 (1979);

(b) T-H. Chan and P. Brownbridge, J. .Am. Chem, Soc., 102, 3534 (1980).

5. (a) M.A. Tius, Tet. Lett., 22, 3335 (1981); (b) M.A. Tius and S. Ali, J.

Org. Chem., 0, 3163 (1982); (c) M.A. Tius and S. Savariar, Synthesis, 467

(1983); (d) M.A. Tius and A. Thurkauf, J. Org. Chem., _, 3839 (1983).

6. R.R. Rastogi, A. Kumar, H. Ila and H. Junjappa, J. Ches. Soco, Perkin Trans

1, 549, 554 (1978) and referentes therein.

7. B. Myrboh, Ho Ila and H. Junjappa, J. Org. Chem., _, 5327 (1983).

8. R.K. Dieter, J.R. Fishpaugh and L.A. Silks, Tet. Lett., 23, 3151 (1982).

(Received in UK 31 July 1984)